The extreme bottom of the outcrop is clean meta-dacite.

The hammer head is in whiteschist - slightly greener and paler in colour

About 1/3 the way up the handle a sharp transition back into meta-dacite crosscutting the main tectonic foliation of the dacite.

The whole rock volume contains abundant free-quartz, which is a major product of the whiteschist process

As the metadacites contain quartz lenses (which are parallel to the main tectonic foliation) and are altered into whiteschist (but after the main def episode), whiteschist formation (ie fluid flow) must have been occurring throughout and slightly after the main deformation episode (which happened at c. 570 Ma).

This is taken as evidence to show in-situ metasomatic alteration of meta-dacites into whiteschist (ie whiteschists as opposed to formation from sediments or evaporite deposits!!.

Picture by Simon Johnson